Banca de DEFESA: NATÁLIA SOARES PRADO

COMMERCIAL GRAPHITE SHEET AS SUBSTRATE FOR ELECTROPOLYMERIZATION OF PHENOTHIAZINE COLORS AND THEIR ELECTROANALYTIC APPLICATIONS

Graphite sheets, electropolymerization, poly(toluidine blue), poly(methylene blue), disposable electrode.

Graphite sheets (GS) have interesting properties, such as high mechanical strength, electrical conductivity, and surface stability, in addition to being produced on a large scale at a low cost. In this thesis, graphite sheets were used as conductive substrates for the electropolymerization of phenothiazine dyes, methylene blue (MB), and toluidine blue (TB), aiming at the development of electrochemical sensors. Electropolymerization was performed by cyclic voltammetry, and it was observed that the switching potential strongly influences the electropolymerization of MB. The switching potential of 1.2 V (Ag/AgCl) resulted in greater roughness of the electropolymerized film. The poly(methylene blue) (PMB) film deposited on the surface of GS increased the sensitivity to nitrofurantoin (NFT) and minimized electrode fouling. The GS/PMB exhibited a linear response range from 5 to 100 μmol L-1, with a detection limit of 55 nmol L-1 . The proposed sensor has been successfully applied for NFT quantification in urine and tap water samples. For the electrode modified with poly(toluidine blue) film (PTB), an improvement in analytical performance was observed when potential cycles in KOH 0.1 mol L-1 were performed after the film growth step. This procedure also resulted in flat and more compact films. The developed sensor showed an increase in sensitivity for tryptamine (TRYP) determination, lower detection limit, and it was less susceptible to the electrode deactivation during TRYP electrooxidation. The GS/PTB-KOH electrode exhibited a linear range from 0.05 to 0.9 μmol L-1 and a detection limit of 12 nmol L-1 allowing for the quantification of TRYP in cheese samples. Model analytes such as procaine (PRO) and lidocaine (LID) were also evaluated to explore the applicability of the sensor and improved sensitivity and lower detection limits were observed. The electropolymerization of phenothiazine dyes in graphite sheets proved to be a promising strategy for fast and inexpensive analysis using a disposable electrode for sensing different analytes.